3D Robotics

Dealing with GPS blocking/jamming


The sad truth is the GPS system is a fragile one, easily blocked and interfered with, as the tragic fatal crash of a drone in South Korea last month (shown above) showed. 

Now DARPA is sponsoring new research to help drones navigate without GPS. Called "All Source Positioning and Navigation (ASPN),” it’s trying to “enable low-cost, robust and seamless navigation solutions … with or without GPS.”

Wired writes:

Right now, the agency notes, the military’s navigation systems primarily rely on a pairing of two devices: GPS, which uses satellite data, and what’s known as an Inertial Navigation System (INS), which relies on “dead reckoning” (using estimates of speed and direction, without external references) to provide locational intel.

It’s a tactic that’s accompanied by several problems. For one, INS — because it uses internal, ongoing estimates — is notoriously error-prone without a GPS system to back it up, so it can’t be relied upon exclusively. And INS systems often obtain their starting position and velocity from a GPS device. Which means if the GPS is under attack, the INS risks leading military personnel (or the drone or weapon they’re navigating) astray.

These navigational systems are also extremely inflexible. Typically, Darpa notes, they’re programmed to accommodate, maybe, one additional sensor (say, a magnetometer) and unable to plug into any others. As a result, personnel can’t respond to “new threats or mission challenges” in real time. Not to mention that, even as consumer navigation tech becomes more sophisticated (Apple Maps, anyone?) the military can’t take advantage of the most cutting-edge products.

Of course, there are already plenty of GPS alternatives available. Radio beacons, which transmit signals from static locations to receiving devices, allow the calculation of location based on proximity to various beacons. Ground feature navigation extracts the positions of tracked objects and then uses them as points of reference to gauge a vessel’s locale. And stellar navigation systems use the coordinates of celestial bodies to assist in a vehicle’s navigation.

Darpa’s dream navigational system would go beyond those kinds of discreet systems — by incorporating pretty much all of them. The ASPN system, according to Darpa’s announcement, should be able to accomodate any available sensor, and be versatile enough to incorporate new sensors “as they become available in the marketplace.” The key benefit to such adaptability would be the mitigation of GPS-dependency. Personnel would instead have myriad sensors at their disposal, and be able to toggle between them as necessary. In other words, a suite of backup tools to work, in conjunction, as a safety net in case of GPS failure. Among the ton of gadgets that Darpa wants the system to utilize: 3-D imagers, LiDAR, temperature sensors … and good old compasses.

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  • How about a DEM of the area stored in a onboard computer and have the Drone compute a model on the fly which it performs a best fit on. Got to be hard to remodel the landscape at the drop of a hat. Not going to work over water tho ...

  • Moderator

    Jake, are you confusing dead reckoning with INS?  (INS may use DR, but it corrects for the inherent DR errors)

    The govt does not actually inject errors into GPS, they previously restricted access to the higher resolution.

    Since the FAA now certifies GPS approaches, I would say they have confidence in it's accuracy. 

  • I think people need to remember that GPS was never meant to be the sole source to base control on.  Anyone basing their entire control scheme on GPS is bound to have problems.

    Dead reckoning should always be the basis for control.  GPS can really add precision and added features, but there should always be a fallback in cases when GPS is wrong or unavailable.

    If your dead reckoning and GPS don't agree there should be some sort of fallback scheme.  It is stupid easy to jam GPS and not terribly difficult to spoof either.

    The government has always said GPS is not to be exclusively trusted and does inject errors for military reasons.  If they decided to inject major errors directly into the system they could and it would shake out all the improperly designed systems that rely entirely on it.  You would have no recourse if they did this and you'd be 100% liable for any damages.

  • I happen to work with commercial aircraft navigation systems. It is apparently common for aircraft flying around Seoul to have their GPSs drop out. Their mischievous neighbors to the north are suspected of playing games. So far it seems they are only jamming and not spoofing. Commercial aircraft primarily rely on GPS for navigating, but they have inertial and radio sensors for backup. Jamming will not cause commercial aircraft to fly off course or drop out of the sky. (Spoofing on the other hand...)

    I am curious what backup to GPS the aircraft in this unfortunate accident was using. I wonder how much of this accident was user error versus poor design versus bad luck.

  • I did it once with a board and a steel rod.  I kept marking before and after noon and the shortest shadow was solar noon.  The equation of time got me in the ballpark for when to expect local solar noon.  I used the shadow length to estimate my latitude and was lucky to get within 40 miles.  Was the board really level?  Was the steel rod really perpendicular?  Was my mark really the end of the shadow?  I was going to try for longitude using a stop watch, but figured my errors wouldnt be any less.   

  • I had the bright idea to use an ArduIMU on an astrolabe/sextant, just to do it nothing else.  A sextant is used to measure angles(ArduIMU measures angles too) above the horizon, so why not.  I've also wondered what it would take to optoelectronically track the sun, maybe a dome that can sense the hottest spot and infer that is the sun.

  • With a well calibrated airspeed and magnetometer, I think a reasonable(better than nothing) dead-reckoning system could be implemented into Ardupilot for fixed wing aircraft. Starting with it's last known position it would try to guide the plane to either where it was going or RTL. While the gps was working, it could constantly update wind estimates and use that in the dead-reckoning calculations when the GPS goes away, and then prevent your plane from flying away and point it in the right direction. 

    I still can't figure out how we lost one in Iran. It must of been far away and had an engine failure and just guided itself to a landing on the way home.

  • Dare i suggest that the members of each country group all team up and point some seriously high power yagis at each other. We could do a DIY positional network :)

    (where legal, of course)

  • Has it been determined that GPS jamming was the cause of the Camcopter crash, or of the loss of the RQ-170 in Iran?  Regardless, I understand the need for alternatives, but in these cases I haven't come across conclusive reports as yet.

  • Having alternative system to GPS sounds even more important after this incident.

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